1. Field of the Invention
This invention relates to a steering wheel provided with a self-aligning mechanism, which, when a force of impact acts on a ring section, makes the plane of the ring section substantially perpendicular to the direction of the force of impact.
2. Description of the Prior Art
FIG. 1 shows a conventional steering wheel provided with a self-aligning mechanism (see Japanese Utility Model Laid-Open No. 60-9764: U.S. Pat. No. 4,709,944, U.S. Pat. No. 3,948,118).
The steering wheel WO includes a steering wheel core member CO comprising core element 4 of a ring section R, core elements 3 of spoke sections S, a boss 1 of a boss section B which is connected to a steering shaft not shown, and a boss plate 2 for connecting the boss 1 and the spoke section core elements 3 together. Each core element of each section is made of steel and connected to other elements by welding.
The boss plate 2 of the steering wheel WO has a plurality of through holes 2a formed around the boss 1, thereby constituting the self-aligning mechanism. That is, the boss plate 2 has deformable portions 2b defined by low-rigidity narrow portions between the through holes 2a, so that when a force of impact acts on the ring section R of the steering wheel WO attached to a steering shaft, the deformable portions 2b undergo plastic deformation. As a result, the plane of the ring section R becomes substantially perpendicular to the direction of the force of impact.
2c designates reinforcing ribs which project upward from the periphery of the boss plate 2 to reliably deform the deformable portions 2b when the force of impact acts on the ring section R. 2d and 2e designate puller holes and mounting holes used in mounting functional components, such as a horn switch mechanism. These holes 2d; 2e also serve like the through holes 2a for defining the deformable portions 2b.
However, since the steering wheel core member CO of the conventional steering wheel WO is manufactured by connecting all the core elements of the individual sections together by welding, the number of manufacturing steps and the manufacturing cost of the steering wheel WO increase.
Further, some overlap width of welding must be included in each core element of each section to weld them with a given strength of welding, leading to a corresponding increase in size of the core member CO; thus, the weight of the steering wheel core member CO and the weight of the steering wheel WO increases.